The present invention relates to adaptive cruise control (ACC) systems where a vehicle equipped with an ACC system tracks a target vehicle and determines whether the target vehicle has changed lanes.
Conventionally, a vehicle having an ACC system follows a preceding vehicle (target vehicle) at a constant distance or headway time. Typically, steering or yaw rate sensor information is used to estimate target vehicle distance and speed if both the target vehicle and the ACC equipped vehicle are in the same straight lane or curved lane. However, when the preceding or target vehicle is changing lanes, an ACC equipped vehicle having a system that relies on steering or yaw rate information will not be able to accurately determine whether the preceding vehicle is changing lanes or whether the preceding vehicle is entering/exiting a curve.
A prior art method for estimating the path of a preceding or target vehicle is disclosed and described in Japanese unexamined patent application No. 4-245600. In the application, the path estimation was determined based on the steering and yaw rate information. However, the estimation of the application is only accurate when an ACC equipped vehicle and the target vehicle are in the same curve or on a straight line. More specifically, if one of the vehicles (ACC equipped or target vehicle) is in a lane having a different radius of curvature, the application""s path estimation method is inaccurate.
Therefore, what is needed is a new and improved system and method for determining whether a preceding or target vehicle is changing lanes. The new and improved method of the present invention should determine whether the preceding vehicle is changing lanes during a transient period, where the lane change occurs or when both vehicles are in different parts of the curve having different curvatures.
In an aspect of the present invention a method for determining whether a target vehicle is changing lanes in a roadway is provided. The method includes measuring an azimuth angle and a range between the target vehicle and a host vehicle, measuring a host vehicle velocity and a host vehicle yaw rate, calculating a relative velocity from the measured azimuth angle, range, host vehicle velocity and host vehicle yaw rate, comparing an absolute value of the calculated relative velocity and azimuth angle to a developed theoretical equation, and determining whether the target vehicle is changing lanes based on the comparison of the absolute value of the calculated relative velocity and azimuth angle to the developed theoretical equation over time.
In another aspect of the present invention, the developed theoretical equation is an equation of an ellipse.
In yet another aspect of the present invention, the developed theoretical equation is a quadratic equation.
In yet another aspect of the present invention the equation of the ellipse describes the relationship between the azimuth angle and relative velocity during a lane change.
In still another aspect of the present invention, comparing an absolute value of the calculated relative velocity and azimuth angle to a developed theoretical equation further includes performing a regression on the calculated relative velocity and measured azimuth angle.
In still another aspect of the present invention determining whether the target vehicle is changing lanes further includes calculating a standard deviation indicating how well the developed theoretical equation fits the measured azimuth angle and calculated relative velocity.